1. Field of the Invention
The present invention relates to a flash control system for remotely controlling a flash-light emission of an external flash device by a light signal output from a camera associated with the external flash device.
2. Description of the Related Art
Conventionally, a flash-light emission of an external flash device is remotely controlled by a camera in accordance with a so-called slave method. Namely, when a flash light is emitted from a built-in flash device of the camera, the emitted flash light serves as a trigger for initiating an flash-light emission of the external flash device.
In this external flash control system, an amount of the flash-light emission of the external flash device cannot be accurately controlled, because only a timing of the flash-light emission of the external flash device is adjusted, with the amount of the flash-light emission being fixed. Thus, it is difficult to provide highly accurate exposure in response to photographing conditions which are variable depending on an object-distance or the like.
In addition, when the external flash device is placed such that the flash-light is laterally emitted from the external flash device with respect to a photographing optical axis of the camera, an undesirable shadow of an object frequently results in a photographed picture. On the contrary, when the external flash device is placed such that the flash-light is emitted from the external flash device along the photographing optical axis, a red-eye effect is frequently caused in a photographed person.
Therefore, an object of the present invention is to provide a flash control system for remotely controlling a flash-light emission of an external flash device by a light signal output from a camera, in which both a timing and an amount of the flash-light emission are properly and accurately controllable, and in which an undesirable shadow of a photographed object and a red-eye effect of a photographed person can be removed from a photographed picture.
In accordance with an aspect of the present invention, there is provided a flash control system for remotely controlling an external flash device by a camera associated with the external flash device. In the control system, the camera includes a first calculator that calculates a first exposure factor for determining an amount of a flash-light to be emitted from a built-in flash device of the camera, and a second calculator that calculates a second exposure factor for determining an amount of a flash-light to be emitted from the external flash device. A total amount of both the flash-light emission of the built-in flash device and the flash-light emission of the external flash devices corresponds to a proper exposure with which an object should be photographed by the camera. The camera further includes a light signal source that emits a light signal, and a light signal controller that controls the light signal source to emit at least two light signals therefrom at a time interval such that the second exposure factor is represented by the time interval between the light signals. The external flash device includes a light signal detector that detects the light signals emitted from the light signal source, and a flash-light emission controller that controls an amount of the flash-light emission of the external flash device in accordance with the time interval between the light signals such that the amount of the flash-light emission of the external flash device coincides with the second exposure factor.
In the flash control system, preferably, the camera further includes a flash-light emission timing calculator that calculates a flash-light emission timing at which the flash-light should be emitted from the external flash device. In this case, the light signal controller further controls an emission of one of the light signals such that the flash-light emission timing is represented by the emission of the aforesaid one of the light signals, and the flash-light emission controller further controls a timing of the flash-light emission of the external flash device in accordance with the emission of aforesaid one of the light signals. Preferably, the control of the timing of the flash-light emission of the external flash device by the flash-light emission controller is based on a last light signal of the light signals.
In the flash control system, the calculations of the first and second exposure factors by the first and second calculators may be based on at least a photometry measurement performed by the camera upon photographing. Also, each of the first and second exposure factors may be calculated as a stop value derived from the photometry measurement performed by the camera.
In the flash control system, preferably, the light signal source comprises a flash lamp of the built-in flash device of the camera.
In the flash control system, the flash-light emission controller of the external flash device may include a light detector that detects the flash-light emission of the external flash device as a reflected light, a first processor that processes the reflected light, detected by the light detector, to produce a first light-quantitative data representing an amount of the reflected light, a second processor that processes the time interval to produce a second light-quantitative data representing the second exposure factor, and a comparator that compares the first light-quantitative data with the second light-quantitative data, such that the flash-light emission of the external flash device is stopped when it is determined by the comparator that the first-quantitative data coincides with the second light-quantitative data. The light detector may comprise the light signal detector for detecting the light signals.
In accordance with another aspect of the present invention, there is provided a camera, which comprises a first calculator that calculates a first exposure factor for determining an amount of a flash-light to be emitted from a built-in flash device of the camera, and a second calculator that calculates a second exposure factor for determining an amount of a flash-light to be emitted from an external flash device remotely associated with the camera. A total amount of both the flash-light emissions of the built-in and external flash devices corresponds to a proper exposure with which an object should be photographed by the camera. The camera further comprises a light signal source that emits a light signal, and a light signal controller that controls the light signal source to emit at least two light signals therefrom at a time interval such that the second exposure factor is represented by the time interval between the light signals.
Preferably, the camera further comprises a flash-light emission timing calculator that calculates a flash-light emission timing at which the flash-light should be emitted from the external flash device. In this case, the light signal controller further controls the emission of the light signals such that the flash-light emission timing is represented by an emission of a last light signal of the light signals.
In the camera, the calculations of the first and second exposure factors by the first and second calculators may be based on at least a photometry measurement performed by the camera upon photographing. The first exposure factor may be calculated as a first stop value derived from the photometry measurement performed by the camera, and the second exposure factor is calculated as a second stop value derived from the first stop value.
When the camera is formed as a lens shutter type camera, a timing of the emission of the last light signal of the light signals coincides with a time at which an aperture of a shutter of the lens shutter type camera reaches an aperture, corresponding to the first stop value, during an opening-action of the shutter.
When the camera is formed as a camera having a focal-plane shutter, a timing of an emission of a first light signal of the light signals coincides with a time, at which a leading shutter curtain of the focal-plane shutter reaches an end position thereof.
Preferably, the light signal source comprises a flash lamp of the built-in flash device of the camera.
The camera may further comprise a flash-light emission controller that controls the flash-light emission of the built-in flash device in accordance with the first exposure factor. In this case, the flash-light emission of the built-in flash device is performed after the flash-light emission of the external flash device is completed in accordance with the second exposure factor, resulting in the photographing of the object with the proper exposure, due to the total amount of both the flash-light emissions of the built-in and external flash devices.
When the camera is formed as a lens shutter type camera, the first exposure factor represents a stop value, corresponding to a flash-light-emission aperture, at which the flash-light emissions of the external and built-flash devices are sequentially started, such that a part of the proper exposure is obtained by the flash-light emission of the external flash device, and such that a remaining part of the proper exposure, based on the first exposure factor, is obtained by the flash-light emission of the built-flash device.
When the camera is formed as a camera having a flash-light detector for detecting a part of the flash-light emission of the built-in flash device as a reflected light, the flash-light emission controller is associated with the flash-light detector to control the built-in flash device, such that a part of the proper exposure, based on the first exposure factor, is obtained by the flash-light emission of the built-flash device, and such that a remaining part of the proper exposure is obtained by the flash-light emission of the external flash device.